1. Field of the Invention
The present invention relates to apparatus and processes for establishing communication through the wall of a well bore tubular, and more particularly, to apparatus and processes for completing a subterranean well, especially to complete a well in and stimulate multiple subterranean zone(s) and/or formations.
2. Description of Related Art
Once a subterranean well bore has been drilled by conventional techniques utilizing a drilling string which has a drill bit secured to one end thereof, the well bore is completed by positioning a casing string within the well bore to increase the integrity thereof and provide a path for producing fluids to the surface. The casing string is normally made up of individual lengths of relatively large diameter metal tubulars which are secured together by any suitable means, for example screw threads or welds. Conventionally, the casing string is cemented to the well bore face by circulating cement into the annulus which is defined between the casing string and the well bore. The cemented casing string is subsequently perforated to establish fluid communication between the subterranean formation and the interior of the casing string. Perforating is conventionally performed by means of a perforating gun which has at least one shaped charge positioned within a carrier, the firing of which is controlled from the surface of the earth. A perforating gun may be constructed to be of any length, although a gun to be conveyed on wireline is usually 30 feet or less in length. The perforating gun is lowered within the casing on wireline or tubing to a point adjacent the subterranean zone of interest and the shaped explosive charge(s) are detonated which in turn penetrate or perforate the casing and the formation. In this manner, fluid communication is established between the cased well bore and the subterranean zone(s) of interest. The resulting perforations extend through the casing and cement a short distance into the formation. The perforating gun is then removed from the well bore or dropped to the bottom thereof. The formation is often stimulated to enhance production of hydrocarbons therefrom by pumping fluid under pressure into the well and into the formation to induce hydraulic fracturing of the formation or by pumping fluid into the well and formation to treat or stimulate the formation. Thereafter, fluid may be produced from the formation through the casing string to the surface of the earth or injected from the surface through the casing string into the subterranean formation.
In some formations, it is desirable to conduct the perforating operations with the pressure in the well overbalanced with respect to the formation pressure. Under overbalanced conditions, the well pressure exceeds the pressure at which the formation will fracture, and hydraulic fracturing occurs in the vicinity of the perforations. The perforations may penetrate several inches into the formation, and the fracture network may extend several feet into the formation. Thus, an enlarged conduit can be created for fluid flow between the formation and the well, and well productivity may be significantly increased by deliberately inducing fractures at the perforations.
Frequently, a subterranean well penetrates multiple zones of the same subterranean formation and/or a plurality of formations of interest, which are hydrocarbon bearing. It is usually desirable to establish communication with each zone and/or formation of interest for injection and/or production of fluids. Conventionally, this is accomplished in any one of several ways. First, a single perforating gun may be conveyed on wireline or tubing into the subterranean well bore and fired to perforate a zone and/or formation of interest. This procedure is repeated for each zone to be treated. Alternately, a single perforating gun is conveyed on wireline or tubing into the subterranean well and the gun is positioned adjacent to each zone and/or formation of interest and selectively fired to perforate each zone and/or formation. In accordance with another approach, two or more perforating guns are positioned in a spaced apart manner on the same tubing, are conveyed into the well and fired. When the select firing method is used and the subterranean zone(s) and/or formation(s) of interest are relatively thin, e.g. 15 feet or less, the perforating gun is positioned adjacent the zone of interest and some of the shaped charges of the perforating gun are fired to selectively perforate only this zone or formation. The gun is then repositioned by means of the wireline to another zone or formation and certain shaped charges are fired to selectively perforate this zone or formation. This procedure is repeated until all zone(s) and/or formation(s) are perforated and the perforating gun is retrieved to the surface by means of the wireline. In the tubing conveyed, spaced gun approach, two or more perforating guns are conveyed into the well bore on the same tubing in a spaced apart manner such that each gun is positioned adjacent one of the subterranean zone(s) and/or formation(s) of interest. Once positioned in the well, the guns may be simultaneously or selectively fired to perforate the casing and establish communication with each such zone(s) and/or formation(s).
If the zone(s) and/or formation(s) which have been perforated by either conventional approach are to be hydraulically fractured, fluid is pumped into the well under pressure which exceeds the pressure at which the zone(s) and/or formation(s) will fracture. However, the fracturing fluid will preferential flow into those zone(s) and/or formation(s) which typically have the greatest porosity and/or the lowest pressure thereby often resulting in little or no fracturing of some of the zone(s) and/or formation(s). Further, considerable expense can be incurred in pumping fluid under sufficient pressure to fracture multiple zone(s) and/or formation(s) penetrated by a subterranean well bore. In an effort to rectify this problem, a procedure has been utilized wherein a perforating gun is lowered into a well on tubing or wireline adjacent the lowermost zone of interest and fired to perforate the casing and zone. Thereafter, the it is necessary to trip out of the well and remove the perforating gun to the surface. Fluid is then pumped into the well at sufficient pressure to fracture or stimulate the lowermost zone. The stimulation fluid may be recovered from the zone just perforated and fractured to inhibit any damage to the zone which may occur as a result of prolonged contact with the fracturing fluid. Prior to perforating and stimulating the next deepest zone of interest, a mechanical device or plug or sand fill is set in the well between the zone just fractured and the zone to be fractured to isolate the stimulated zone from further contact with fracturing fluid. This procedure is repeated until all zone(s) and/or formation(s) are perforated and fractured. Once this completion operation is finished, each plug must be drilled out of or otherwise removed from the well to permit fluid to be produced to the surface through the well. However, the necessity of tripping in and out of the well bore to perforate and stimulate each of multiple zone(s) and/or formation(s) and the use of such plugs to isolate previously treated zone(s) and/or formation(s) from further treatment fluid contact is time consuming and expensive. In view of this, multiple zone(s) and/or formation(s) are often stimulated at the same time even though this results in unacceptable of treatment of certain zone(s) and/or formation(s). Thus, a need exists for apparatus and processes to perforate casing which is positioned within a subterranean well bore which eliminates the need to run perforating equipment in and out of the well when completing multiple zone(s) and/or formation(s).
Accordingly, it is, an object of the present invention to provide a method and apparatus for economically and effectively perforating and stimulating multiple subterranean zone(s) and/or formation(s) which are penetrated by a subterranean well.
It is another object of the present invention to provide a process and apparatus for completing a subterranean well wherein casing is perforated to provide for fluid communication across the wall of the casing by means of a perforating gun assembly located in a subterranean well bore outside the casing.
It is a further object of the present invention to provide a process and apparatus wherein for completing and stimulating a cased, subterranean well bore wherein entry into the well bore to effectuate completion and/or stimulation is obviated.
It is still another object of the present invention to provide a process and apparatus for expeditiously treating and/or stimulating each subterranean formation penetrated by a subterranean well bore individually and therefore economically.
It is a still further object of the present invention to provide a process and apparatus for completing a subterranean well wherein multiple perforating gun assemblies are positioned in the well bore external to casing and adjacent to multiple subterranean formations of interest and selectively detonated to establish fluid communication between a subterranean formation and the interior of the casing.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, one characterization of the present invention may comprise a process for establishing fluid communication. The process comprises positioning at least one explosive charge in a subterranean well bore such that the at least one explosive charge is placed external to casing which is also positioned within the well bore and is aimed toward the casing and detonating the at least one explosive charge so as to perforate the wall of the casing at least once.
In another characterization of the present invention, a process is provided for completing a subterranean well bore which comprises penetrating the wall of a casing which is positioned and cemented within a subterranean well bore from the exterior of the casing to the interior.
In yet another characterization of the present invention, a process is provided for completing a subterranean well which comprises positioning at least one explosive charge in a subterranean well bore outside of casing and detonating the at least one explosive charge so as to perforate the casing.
In yet another characterization of the present invention, a process is set forth for providing fluid communication across the wall of a casing. The process comprises detonating a first perforating gun assembly which is positioned outside of a casing in a subterranean well bore thereby perforating the casing.
In a further characterization of the present invention, a process is provided for completing one or more subterranean formations. The process comprises detonating a first perforating gun assembly which is positioned outside of a casing in a subterranean well bore thereby perforating the casing and a first subterranean formation.
In a still further characterization of the present invention, a process is provided for completing a subterranean well which comprises penetrating casing which is positioned in a subterranean well bore while the interior of the casing remains unoccupied by perforating guns or other equipment, tools, tubulars or lines.
In a still further characterization of the present invention, a subterranean completion system is provided which comprises a casing which is at least partially positioned within a subterranean well bore and at least one perforating gun assembly which is positioned external to the casing and within the well bore. The perforating gun assembly has at least one explosive charge aimed in the direction of the casing.
In a still further characterization of the present invention, a completion system is provided which comprises a casing and at least one perforating gun which is connected to the exterior of the casing and has at least one explosive charge aimed toward the casing.